Draw a shape. Watch circles reconstruct it.
Any closed curve can be decomposed into a sum of rotating circles — epicycles. Each circle corresponds to a frequency in the Discrete Fourier Transform of the path.
The radius of each circle is the amplitude of that frequency component. Its rotation speed is the frequency. Its starting angle is the phase. Stacked together, they trace the original shape.
Drag the epicycles slider to see how few circles are needed to approximate the shape, or how many it takes to get it exact.